1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to improvement for increasing the radiation property.
2. Description of the Background Art
FIG. 20 is a top plan view of a conventional semiconductor device which forms the background of the present invention, and FIG. 21 is a vertical section view of the same semiconductor device. FIG. 20 also shows the interior of the semiconductor device in a perspective manner. This semiconductor device 151 comprises a substrate 91, insulation layers 92, 93, a heat generating layer 94, plugs 95, 96 and wiring layers 97, 98.
The substrate 91 is a silicon substrate containing boron at a concentration of about 1×1015 cm−3. The insulation layer 92 is an oxide film of about 300 nm in thickness formed on the substrate 91 as an element separating insulation film. The heat generating layer 94 is selectively formed on the insulation film 92 as a resistor, and made of phosphorous-doped poly-silicon containing phosphorous at a concentration of 1×1020 to 5×1021 cm−3. The insulation layer 93 is an interlayer insulating film of 500 nm to 1 μm in thickness formed on the insulation layer 92 so as to cover the heat generating layer 94. The insulation layer 93 is usually formed as a combination layer having a non-doped oxide film and a boron/phosphorous-doped oxide film. The wiring layers 97, 98 are wiring layers patterned on the insulation layer 93 and are formed as combination films containing AlCu.
The plugs 95, 96 are conductors filled in contact holes penetrating through the insulation layer 93, and made of tungsten. The plug 96 connects one end of the heat generating layer 94 and the wiring layer 98, and the plug 95 connects the other end of the heat generating layer 94 and the wiring layer 97.
In the semiconductor device 151 configured as described above, as the power to be applied to the heat generating layer 94 serving as a resistance body is increased, the temperature of the heat generating layer 94 increases as shown in the graph of FIG. 22. When this temperature exceeds the maximum operation temperature Tjmax, electro migration occurs in the wiring layers 97, 98, or reliability of the insulation layers 92, 93 decreases, resulting in deterioration of the performance of the device.
The relationship of ΔT=θ·P is satisfied between the power P to be applied and the temperature rise ΔT. In the above relationship, “θ” is referred to as heat resistance. Therefore, for suppressing the temperature rise ΔT, it is necessary to lower the heat resistance θ by improving the radiation property. Conventionally, for lowering the heat resistance “θ”, there has been an approach that the radiation area is enlarged without changing the resistance value by enlarging the width and length of the heat generating layer 94 at the same ratio. However, this approach had a problem that miniaturization of the semiconductor device 151 is inhibited.